Inhibition of late Na + current, a novel target to improve diastolic function and electrical abnormalities in Dahl salt-sensitive rats

Late Na current (INaL) is enhanced in myocytes of animals with chronic heart failure and patients with hypertrophic cardiomyopathy. To define the role of INaL in diastolic heart failure, the effects of GS-458967 (GS-967), a potent INaL inhibitor on mechanical and electrical abnormalities, were determined in an animal model of diastolic dysfunction. Dahl salt-sensitive (DSS) rats fed a high-salt (HS) diet for 8 wk, compared with a normal salt (NS) diet, had increased left ventricular (LV) mass (1,257  96 vs. 891  34 mg) and diastolic dysfunction [isovolumic relaxation time (IVRT): 26.8  0.5 vs. 18.9  0.2 ms; early transmitral flow velocity/early mitral annulus velocity (E/E’) ratio: 25.5  1.9 vs. 14.9  0.9]. INaL in LV myocytes from HS rats was significantly increased to 0.41  0.02 from 0.14  0.02 pA/pF in NS rats. The action potential duration (APD) was prolonged to 136  12 from 68  9 ms in NS rats. QTc intervals were longer in HS vs. NS rats (267  8 vs. 212  2 ms). Acute and chronic treatment with GS-967 decreased the enhanced INaL to 0.24  0.01 and 0.17  0.02 pA/pF, respectively, vs. 0.41  0.02 pA/pF in the HS group. Chronic treatment with GS-967 dosedependently reduced LV mass, the increases in E/E’ ratio, and the prolongation of IVRT by 27, 27, and 20%, respectively, at the 1.0 mg·kg1·day1 dose without affecting blood pressure or LV systolic function. The prolonged APDs in myocytes and QTc of HS rats were significantly reduced with GS-967 treatment. These results indicate that INaL is a significant contributor to the LV diastolic dysfunction, hypertrophy, and repolarization abnormalities and thus, inhibition of this current is a promising therapeutic target for diastolic heart failure.